(1) Field of the Invention
The invention relates to a method for contactless determination of forces and/or moments acting on a hollow cylindrical body and a measurement arrangement for implementing a related method.
(2) Description of Related Art
Although the method according to the invention and the measurement arrangement according to the invention can fundamentally be used for a plurality of different applications, their use as a strut moment measurement system (MMS), i.e., as a system for determining the bending moments acting on the main rotor strut of a helicopter, is presented in detail below.
In an unarticulated construction of the helicopter rotor head in conjunction with partially elastic rotor blades of fiber composite material, high bending moments are delivered into the rotor strut due to the greater virtual joint distance. Overly high bending moments can lead to premature fatigue of the rotor strut or damage of transmission parts. Therefore, the strut moment in flight operation is monitored with a strut moment system (MMS). The moment or a portion of the maximum allowable moment is displayed to the pilot in the cockpit. Exceeding fixed boundary values in operation leads to maintenance operations and should be avoided.
The prior art is currently to measure the strut moment using foil strain gauges (DMS) that are cemented in the upper part of the rotor strut by means of a cement connection.
In operation, the DMS and the cement connection are exposed to dynamic loads and fluctuating ambient conditions (temperature, vibrations, and moisture) and thus are highly stressed. In a defect of the DMS, due to the poor accessibility of the DMS within the rotor strut and due to the complex cementing process, repair is very time-consuming and costly.